This application relates to the manufacture of projectiles for use in small bore gun ammunition and to the projectiles obtained thereby.
In the present application xe2x80x9csmall-borexe2x80x9d weapons are defined as those weapons of .50 caliber or smaller caliber. The weapon may be a pistol or rifle which includes a rifled barrel.
As used herein, the term xe2x80x9cheavy metalxe2x80x9d refers to a metal having a density greater than the density of lead and the term xe2x80x9clight metalxe2x80x9d refers to a metal having a density equal to or less than the density of lead. xe2x80x9cHeavy metal-basedxe2x80x9d, as used herein, refers to a product which comprises a significant portion, commonly 50% but can be as low as about 20%, by weight, of a heavy metal.
A projectile for a small bore, i.e., .50 caliber or less, weapon having a rifled barrel, commonly, has heretofore been formed from lead. Lead, and similar soft metal projectiles tend to leave deposits of the metal within the barrel of a weapon as the projectile is propelled along the barrel during firing of the weapon. In such jacketed lead-based projectiles, the trailing end of the lead is not fully covered by the inwardly folded open end of the jacket so that this end of the lead is exposed to the heat and pressure of the burning powder of an ammunition cartridge. Under these circumstances, a portion of the trailing end of the lead is volatilized and eventually condenses in the gun barrel, leaving the barrel fouled with lead. In the prior art, it has been a common practice to encase the lead projectile in a copper jacket to eliminate contact of the lead with the lands and/or inner wall of the weapon barrel, and thereby eliminate the lead deposits within the barrel. These copper jackets are commonly preformed, loaded with a lead core, and thereafter die formed to shape the core and jacket into the desired geometry for the projectile. Lead, being highly malleable, readily deforms to the contour of such dies without fracturing. It has also been practiced to electroplate a copper coating on the exterior surface of a lead core. U.S. Pat. No. 5,597,975 references certain prior copper-plating art and discloses a further plating process for ammunition projectiles. Notably, the cores of these prior art projectiles are not intended to be frangible, hence they generally generate only a channel into or through a target. These projectiles, therefore, have less than desired ability to deliver a stopping force to a moving target, such as an animal.
In known prior art jacketed ammunition projectiles, it has been the intent that the jacket play a material part in the destructive force delivered by the projectile to a target, e.g., the terminal ballistics of the projectile. Accordingly, in the prior art, commonly the jackets are locked onto the core by various mechanical interlocks between the jacket and core, such as channelures and other spatially separated indentations in the core and overlying jacket. In similar manner, heretofore, the prior art teaches that the coating applied to a core for use in forming projectiles should perform a destructive function upon the projectile striking a target. Hollow point type projectiles are of this type. Thus, in some prior art coated or jacketed lead-based projectiles, the jacket or plate coating is scored or otherwise treated to encourage the jacket or coating to fragment upon the projectile striking a target and thereby enhance the xe2x80x9cstopping powerxe2x80x9d (ie., terminal ballistics) of the projectile. Even under these circumstances, the lead core does not materially fragment.
Because of environmental concerns relating to lead, much effort has been expended in the development of projectiles which do not contain lead. This effort has attempted to fabricate a projectile which, when fired from a weapon, responds as nearly like a lead projectile as possible. By this means, there need be little or no change in either existing guns or in the ammunition for these existing guns. Further, there is little or no need to retrain shooters in the use of new and different ammunition. Metals having a density greater than the density of lead generally do not lend themselves to known manufacturing techniques for projectiles for gun ammunition. In part, the expense associated with working with such metals has led to the use of powders of heavy metals. These powders, in general, are difficult to form into shapes. Combinations of various heavy metal powders with lighter metal powders that function as binders for the heavy metal powders have been suggested. Among these combinations it has been suggested that tungsten powder be combined with tin powder and cold-pressed into a projectile, such as in U.S. Pat. No. 5,760,331. Other similar powder combinations have been suggested. Coating or plating the individual powder particles has also been suggested to obtain enhanced packing of the powder particles in a die or to render these individual powder particles non-abrasive. These projectiles suffer various deficiencies including, among others, abrasion of the barrel of the weapon including abrasion and eventual failure of the gas system employed to operate the bolt of an automatic or semi-automatic weapon, inaccuracy of flight to a target, inconsistency of performance from projectile to projectile, high cost of manufacture, incomplete frangibility, etc.
Aside from the reported adverse effects of lead projectiles, in certain shooting situations, such as competitive shooting, sport shooting, and certain warfare and/or law enforcement situations, there has developed a need for a projectile of special properties. For example, accuracy of delivery of the projectile from a weapon to a target has always been a concern of shooters of all classes. Wind effects upon a projectile during its free flight to a target can seriously divert a projectile from its desired flight path, the degree of diversion for a given projectile being a function of the strength and direction of the wind, among other factors. It is known in the art that a heavier projectile offers greater resistance to its flight deviation due to wind effects, but heavier projectiles for a given caliber present other problems. For example, heavier projectiles of a given caliber can be made larger (i.e. longer), but to enable a round of ammunition to be chambered in a given caliber weapon, especially in automatic or semi-automatic guns where the overall length (OAL) of a cartridge must be compatible with the magazine for the gun and the chambering mechanism for the gun, the overall length of the round cannot exceed a given standard value, so that any extra length of a heavier projectile must be disposed within the interior of the case of the round of ammunition. This reduces the space available with the interior of the case which is available to receive gun powder. Less gun powder and a heavier projectile result is a slower moving projectile which, in turn, results in several shooting disadvantages, among which is the fact that the projectile will more easily be adversely affected by wind and static air penetration factors, and the projectile will assume a more pronounced trajectory in its travel to a target and will strike the target at a relatively lower velocity, and with reduced terminal ballistics, for example. Further, spin stability of such projectiles becomes a major factor with respect to the accuracy of the flight of the projectile to its target, in some instances requaireing the barrel of the weapon to be provided with a greater twist value that will ensure spin stability of the projectile.
Alternatively, heavier projectiles of a given caliber can be fabricated from a metal that is heavier than lead. Uranium, tungsten, tantalum and tungsten carbide, for example, have been suggested candidates for heavy projectiles. Herein the term xe2x80x9cheavy metalxe2x80x9d is intended to include carbides of the metal unless the context of use clearly indicates otherwise. These metals and their carbides are difficult and expensive to fabricate into a projectile, hence, as noted above, powder metallurgy techniques have been suggested for fabricating powdered heavy metals into projectiles. But, these heavier metal powders are hard, abrasive and have a high melting point. In general, in the absence of inordinately high temperatures, such as sintering temperatures, it has not heretofore been known how to form the powder into self-supporting bodies without the use of a softer, less dense binder. Lead, tin, bismuth, iron and other relatively soft metal powders have been suggested as binders. When using a binder, the resulting prior art projectiles have not exhibited full frangibility, particularly where the metal powders are sintered. Further, in these prior art heavy metal/binder compacts, the heavy metal particles remain exposed on the outer surface of a compressed projectile where they are available to erode and damage the bore of a gun barrel. Commonly, the compressed projectile is encased within a soft metal jacket. This jacket serves to isolate the abrasive core of the projectile from the bore in much the same manner that copper-plated lead projectiles serve to prevent the deposit of lead within the bore of a weapon. In those known instances in the prior art where a projectile core is provided with either a jacket or a plated coating, the jacket or plate is solid and only breaks apart under very large force, and its breaking apart is in the form of relatively large strips or chunks of the jacket, as opposed to being fully frangible. The common copper-clad hollow point .22 caliber lead projectile is an example. These prior art cores are solid or essentially solid (e.g., sintered), and perform as if they were a solid metal body.
In certain shooting situations, it is desired that the projectile disintegrate upon striking a semi-solid or solid target, preferably with little or no trace of the projectile remaining on the target. This action primarily is intended to prevent the projectile from ricocheting and endangering a secondary target. Other terminal ballistic features of frangible projectile relate to their destructive capacity. These desired characteristics suggest a powder-based projectile. However, the prior art teaches that to provide a heavy metal powder-based projectile, one must employ inordinately high pressures and/or sintering, to develop appropriate and sufficient bonding between the powder particles as will allow the compacted body to withstand mechanical handling in various manufacturing operations, which will be of uniform density, and which will not disintegrate in flight due to the tremendous centrifugal forces imposed upon the projectile when fired from a rifled gun barrel. Thus, bonding of the particles to one another, such as with a binder or by sintering, is antagonistic to a desired disintegration of this same body upon it striking a target.
In certain law enforcement or warfare circumstances, it is highly desirable that a fired projectile does not ricochet. Ricocheting projectiles endanger both friendly forces and innocent bystanders. In these circumstances, it also is desired that the projectile produce both a xe2x80x9cstopping effectxe2x80x9d and be lethal.
As noted hereinabove, the known prior art coatings and/or jackets for solid core projectiles teach that the coating or jacket should adhere to the core and only fragment in the form of large chunks or pieces which allegedly increase the destructive power imparted to a target upon it being struck by the projectile. In the instance where the projectile desirably is frangible, the prior art jackets and coatings for cores are not known to disintegrate into relatively minute particulates, hence are less than desirable for use where full frangibility of the projectile is desired or required.
U.S. Pat. No. 5,594,186 (the ""186 patent) presents what is represented to be the state of the art in powder metallurgy with reference to the attainment of high density metal products fabricated from metal powder(s). This patent lists xe2x80x9cfour basic steps to convert a metal powder into a metal component, namely: (1) preparation of a metal powder mixture (said to typically include a metal powder and a lubricant for minimizing xe2x80x9cfriction between the metal powder and the tooling during compaction, or pressing, stepxe2x80x9d), (2) pressing the powder mixture in a die to form a green compact, (3) after pressing, subjecting the green compact to an elevated temperature to form a metal component, ie., sintering, and (4) optional secondary operations, such as deburring, to provide the final finished metal component. The strength of a metal component is stated in this patent to be xe2x80x9cdirectly related to the density of the metal component, which in turn is directly related to the density (strength) of the green compact so that considerable effort has been expended in searching for ways to increase the density of both the green compact and the metal component toward 100% of theoretical density. In this regard it is noted that with spherical powder particles one can achieve a theoretical density of between about 88% and 92%. Repressing and sintering of a green compact can raise the theoretical density to about 95%. Warm pressing of the green compact, followed by sintering can achieve about 95% theoretical density. Hot isostatic pressing is said to achieve about 96% of theoretical density. As noted in this patent, each of these processes is expensive and/or time consuming. Justification for the use of such processes in achieving 95%-96% theoretical density of a metal component can only be for special situations and components. In the process of the ""186 patent, a metal powder is mixed with a lubricant, loaded into a die and pressed at preferably between about 80,000 to 120,000 psi to form a green compact having a density of 95% to 96%. Thereafter, the green compact is heated to about 300xc2x0 C. to about 400xc2x0 C. to volatilize or otherwise drive off the lubricant, followed by heating of the green compact to its sintering temperature.
The metal powder of this patent is characterized as being xe2x80x9csubstantially linear, acicular particles having a substantially triangular cross sectionxe2x80x9d. They are further noted to xe2x80x9chave a length of about 0.0006 inches to about 0.20 inch, a base of about 0.002 to about 0.05 inches, and a height of about 0.002 to about 0.05 inchesxe2x80x9d, preferably a length of about 0.01 to about 0.18 inches, a base of about 0.003 to about 0.04 inches, and a height of about 0.004 to about 0.035 inches, and an aspect ratio (length to base ratio) of at least 3 to 1, preferably 5 to 1. Of the three longitudinal surfaces of each particle, one is said to be convex, one is concave and the third is planar or concave. These characteristics of the metal powder particles are stated to provide improved deformation and interlocking between metal particles in the die. Notably, the particles of this patent are not to approach a spheroidal geometry. Production of the required metal powder particles is by means of xe2x80x9ca machining or milling process wherein a block or sheet of the metal is fed through a carbide mill or a high-speed steel end mill. The mill has serrated flutes, or inserts, which determine the length of the acicular metal particles. The other dimensional and geometrical properties of the metal particles are determined by the mill speed, metal feed rate, and depth of cut.xe2x80x9d Thus, the powder particles of this patent have a relatively narrow size distribution, which size is limited to the length, width and height ranges specified. This process is very costly and time consuming, thereby causing the cost of the metal powder to be excessive for other than special applications. Certainly, it is impractical as the source of metal powder particles for use in the fabrication of millions of gun ammunition projectiles which must be of low individual cost. More importantly, the projectile produced as taught in the ""186 patent is not fully frangible. Rather it is the objective of the ""186 patent to produce a strong projectile, not a frangible projectile. The present inventor has discovered that one can provide a fully frangible projectile by a method which eliminates the time-consuming and costly powder metallurgy techniques taught in this patent.
Aside from his own work with powder-based cores, the present inventor is not aware of any successful fully frangible metal powder-based projectile which can be fire accurately form a small bore weapon. xe2x80x9cFully frangiblexe2x80x9d, as the term is employed with respect to ammunition projectiles, is defined as being disintegratable, upon impact of the projectile with a semi-solid or solid target, into individual particulates, substantially all of which are of a size on the order of the particle size of that powder in the core that has the largest particle size. Most commonly disintegration occurs when a projectile impacts a solid or semi-solid target. In some instances full disintegration may occur over a finite distance after the initial impact with a target, depending upon the medium through which the projectile is traveling. For example, when a projectile of the present invention strikes a gel block, it initially penetrates the gel block for a short distance and then disintegrates within the gel block, the particles of the disintegrated projectile fanning out and traveling in substantially all directions radially in a generally conical pattern from the point of commencement of the disintegration until their kinetic energy is spent. In other instances, such as when the projectile strikes a cold rolled steel metal sheet at an angle of about 90 degrees (ie., the path of the projectile is about normal to the plane of the metal sheet), the projectile commences disintegration upon initially striking the metal sheet, continues disintegration as it passes through the sheet, creating a channel through the sheet and which has a diameter substantially greater than the diameter of the projectile, and then within a few inches after passing through the sheet, the powders of the disintegrated projectile lose all their momentum and fall harmlessly under only the influence of gravity.
It is therefore an object of the present invention to provide a method for the fabrication of frangible projectiles for use in gun ammunition for small bore weapons wherein the individual projectiles may be produced in large numbers and at relatively low individual cost.
It is another object of the present invention to provide a method for the manufacture of frangible projectiles for gun ammunition wherein the method is adaptable to the manufacture of projectiles having selectable performance characteristics.
It is another object of the method of the present invention to provide frangible projectiles for gun ammunition wherein the projectiles may be made to exhibit substantially full penetration of selected targets followed by substantially full frangibility, or to exhibit full frangibility, upon the projectile striking a selected target.